BACKGROUND A hall mark of human cancer, particularly solid tumor, is aneuploidy. Through a synthetic lethal screen with the Ras oncogene we have found that Ras mutant cancer cells exhibit increase mitotic stress. PURPOSE To study the effect of Ras mutation in mitosis and in chromosomal segregation. To understand the mechanisms by which mutant Ras affects the mitotic machinery. SIGNIFICANT MATERIALS AND METHODS We will use inducible Ras constructs to study its effect in cells that are synchronized to enter mitosis. FY2010 ACCOMPLISHMENT We have established constructs to expression Ras proteins in an inducible fashion.